Prolyl endopeptidase (PEP; EC 3.4.21.26; also called prolyl oligopeptidase) is a serine peptidase characterized by oligopeptidase activity. It is the name giving enzyme of family S9A, prolyl oligopeptidases, in clan SC (1). Enzymes belonging to clan SC are distinct from trypsin- or subtilisin-type serine peptidases by structure and by order of the catalytic triad residues in the primary sequence (2;3). The recently reported three dimensional structure of PEP revealed a two domain organization (4). The catalytic domain displays an α/β hydrolase fold in which the catalytic triad (Ser554, His680, Asp641) is covered by a so-called β-propeller domain. Most likely, the propeller domain controls the access of potential substrates to the active site of the enzyme and excludes peptides having more than 30 amino acids.
Despite a profound knowledge of the enzymatic and structural properties of PEP, the biological function of this enzyme is far from being fully understood (5;6). Highly conserved in mammals, PEP is ubiquitously distributed, with high concentrations occurring in the brain (7). Recently, the enzyme gained pharmaceutical interest due to a reported cognitive enhancement induced by treatment with specific PEP inhibitors. In rats displaying scopolamine-induced amnesia, PEP inhibition caused acetylcholine release in the frontal cortex and hippocampus (8). Furthermore, administration of a PEP inhibitor in rats with middle cerebral artery occlusion prolonged passive avoidance latency and reduced the prolonged escape latency in the Morris water maze task (9). The potential of PEP inhibitors as antidementia drugs was further confirmed by reports of neuroprotective effects. Inducing neurodegeneration in cerebellar granule cells led to increased neuronal survival and enhanced neurite outgrowth in presence of a PEP inhibitor (10). Moreover, the level of m3-muscarinic acetylcholine receptor mRNA was found to be increased after PEP inhibition. This resulted in a stimulated phosphoinositide turnover.
It has been hypothesized that these effects are due to modulation of neuropeptide bioactivity by PEP (11). In vitro, PEP is able to rapidly inactivate several neuropetides, including substance P and arginine-vasopressin (AVP) by limited proteolysis (12;13). Neuropeptides, such as substance P or AVP are known to influence learning and memory (14;15). The administration of substance P can induce long-term potentiation (LTP), a well established parameter for learning and memory (16). Binding of substance P to neurokinin 1 receptor stimulates a G-protein mediated increase in IP3 concentration and a release of Ca2+ from intracellular stores within the endoplasmic reticulum (ER) (17;18). It is well established, but untested for substance P, that Ca2+ release from these stores is implicated in the induction of LTP and in learning and memory (19). In postsynaptic cells, LTP is prevented by the inhibition of IP3 receptors, demonstrating the crucial role of IP3 formation and Ca2+ release in this learning and memory model (20). It should be noted, however, that PEP is primarily located in the cytosol (21), whereas the interaction between the neuropeptides and their receptors takes place on the cell surface. Recently, Hasebe et al. found, that cytosolic prolyl endopeptidase is involved in the degradation of p40-phox splice variant protein in myeloid cells (22).
EP 0 172 458 discloses N-phenyl alkanoyl pyrrolidine derivatives useful as anti-amnesic agents.
EP 0 359 547 discloses pyridine compounds inhibiting prolylendo peptidase activity and useful for the treatment of amnesia.
U.S. Pat. No. 5,340,832 discloses N-substituted carbamoyl-alkanoyl-prolinal derivatives useful as inhibitors of prolyl endopeptidase for treating amnesia.
U.S. Pat. No. 5,763,576 discloses tetrapeptide alpha-ketoamides as selective and total inhibitors of serine and cysteine proteases. These compounds are useful in the treatment of tissue damage and various inflammatory conditions, such as blistering, and in the treatment of neurodegenerative diseases such as ischemia, stroke and Alzheimer's disease. The compounds are also inhibitors for blood coagulation enzymes and are useful anticoagulants for the treatment of thrombosis.
WO 91/18891 discloses aromatic pyrrolidine and thiazolidine amide(s) as prolyl endopeptidase inhibitors, which are useful for treating CNS disorders such as various memory or learning dysfunctions associated with disease e.g. Alzheimer's disease; amnesia; dementia; anxiety; ischemia; and damage caused by stroke.
WO 94/12474 discloses cyclic ketone compounds as prolyl endopeptidase inhibitors-including two nitrogen-containing heterocycles linked by a carbonyl group. These compounds inhibit the degradation and deactivation of TRH, substance P, neurotensin and vasopressin. They are useful for the treatment and prevention of amnesia and of dementia including Alzheimer's disease.
WO 95/03277 discloses N-substituted pyrrolidinyl-oxo-acetamide compounds as protease (especially PEP) inhibitors useful for treating memory loss e.g. Alzheimer's disease, and auto-immune disorders.
WO 95/15310 discloses prolyl peptide derivatives as prolyl endopeptidase inhibitors. These compounds can be used as memory enhancing agents to improve mental capacity, ability to recall cognitive events, and learned motor activities. Thus the compounds of WO 95/15310 may be used in patients suffering from aphasia, apraxia, agnosia, or any type of amnesias, benign forgetfulness and Korsakoff's syndrome. The compounds may also be used to prevent or slow memory deficits.
WO 97/07116 discloses PEP inhibitors for the use in treatment of acute events (such as ischemia and hypoxia) and progressive neurodegenerative disorders, including Alzheimer's disease, AIDS dementia and Huntington's disease.
WO 98/35960 discloses PEP inhibitors useful as nootropics having memory enhancing and anti-amnesic effects useful in the treatment of age-related cognitive decline and neuroprotectants useful for treatment of acute events (ischemia/hypoxia) and progressive neurodegenerative disorders such as Alzheimer's disease, AIDS related dementia and Huntington's disease.
WO 00/09542 discloses Alpha-keto heterocycles inhibiting the enzymatic activity of a serine proteases. The compounds can be used to inhibit microbial growth, reduce perioperative blood loss, preserve transplantation tissues or organs, inhibit cancer cell growth or tumour progression or tumour metastasis or invasion, treat pulmonary vascular disease, restenosis or pulmonary hypertension myocarditis, bronchopulmonary dysplasia, myocardial necrosis or post-cardiac transplant coronary arteriopathy, atherosclerosis, reperfusion injury, Alzheimer's disease, hypoxia, ischemia and blood coagulation disorders.